Moulds are microscopic fungi that can be found almost anywhere, both indoors and outdoors. Mould growth occurs mainly in warm, damp, and humid conditions. They reproduce by making spores that are released into the air to be transported to other places where they can germinate and grow. When mould is in an active growth phase, it releases gases into the air called Mould Volatile Organic Compounds (MVOCs). Not all of these gases can be detected by smell.
Moulds can grow on wood and insulation, in carpet, and even behind walls where they can continue to grow undetected. When excessive moisture accumulates in the home, mould growth will often occur. This moisture build-up can stem from plumbing leaks, condensation in air conditioning and heating systems, or from ground water penetration as well as many other sources. If damp or wet drywall becomes moist and is not dried out within two days, mould can be suspected to be growing within the walls, even if it is not visible.
When mould is present in large quantities, it can present a health hazard, potentially causing allergic reactions and respiratory problems in people who have sensitivities to mould. Moulds produce substances that cause hay fever-type symptoms such as a runny nose, itchy eyes, sneezing, and skin rashes. These reactions can happen immediately upon exposure, or they can be delayed. More severe reactions may occur in people who have mould allergies, and may include fever and shortness of breath. In addition, moulds can trigger asthma attacks in people with asthma and who are allergic to mould. Some people with chronic lung illnesses can develop infections in their lungs with prolonged exposure to mould in the home.